Emissions from stationary and mobile fossil burning devices have been and will continue to be of particular concern in view of accumulating laws and regulations restricting emissions from such devices. In one aspect, particulate matter within emission has been regulated causing industries, particularly the automotive industry, to utilize particulate matter removal devices. Such removal devices are configured to catch or trap particulate matter flowing through an exhaust gas stream prior to exiting an exhaust system of the emission generating device.
In another aspect, filters are used for removal of such particulate matter from exhaust gas streams, such as those generated by diesel engines, gasoline engines or otherwise. To determine when the particulate matter filter is reaching its capacity, the total volume or volume flow rate of particulate matter flowing into the filter or within the exhaust gas stream is monitored. This monitoring is often achieved through a particulate matter sensor exposed to the exhaust gas flow. In this configuration, the particulate matter sensor includes a probe extending into the exhaust gas flow. Some exhaust gas sensors function by transmitting signals based upon a resistance across the probe of the sensor for example, as particulate matter builds up across the sensor, the resistance changes thereby varying the output of the probe and accordingly providing an indication of the amount of particulate matter that has traveled past the sensor and into the filter.
However, many of these sensors fail to provide accurate readings of particulate matter flowing past the sensor or within an exhaust gas stream. For example, many of these sensors are not sufficiently robust to withstand forces or temperatures encountered by such sensors. Other problems with these sensors are their inability to accurately indicate the presence of particulate matter within an exhaust gas flow due to poor signal noise ratio and accumulation of particles on the sensor and other similar deficiencies. Still other problems exist as well.
Accordingly, in view of the shortcomings of previous sensor designs, as described above, there is a need for improved methods and devices for monitoring the flow of particulate matter flowing within and exhaust gas stream.